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The 1st 7.2 AVR was the HK 745. It has 2 subwoofer outputs, but note each output is different as to deliver a smoother low frequency response by minimizing the room's resonances & nulls..

The 745 was introduced about 2 years ago. Be careful certain brands like Yamaha have AVRs with 2 subwoofer outputs and they claim it to be 7.2, both outputs are simply wired in parallel. One can do the same thing with an RCA Y adapter available from Radio Shack for $1.49 and works on any AVR with a subwoofer out jack..

Someone already posted that we can do .2 just using a Y-cable and that is all 7.2 is! Dont be fooled into spending more money on 7.2 AVRs and do not even bother worrying about 7.2 at all. Its a waste of discussion, time and money.

I have 4 subs in a room to all requiring a connections, my sub has one Sub out RCA connection but I easily wire them all up properly. Also, sub calibration should ALWAYS be done outside of any Pre/pro or AVR using the proper sub EQing products available and posted all the time in the DIY sub or Subwoofer forums.

The SMPTE Digital Cinema document that 'underlies' the HDMI AudioFrame specs, plus Blu-Ray, dts, and Dolby eight channel audio implementations, actually contains references to 20 'standardized' speaker locations including two distinct LFE channels (which I have only seen described as LFE and LFE2.) [The addition of a second LFE channel might have been influenced by Tomlinson Holman's 10.2 speaker configuration experiments and theater implementations.]

It appears that dts is not allowing/supporting the authoring of any two LFE channel speaker mixes at present [and I have not seen enough eight channel details from Dolby to form an opinion...]

So [maybe?] we could THEORETICALLY have Blu-Ray disks authored with a 6.2 or 5.2 channel mix -- but any receiver not specifically configured to output two separate lfe channels should just perform a [lossless] remap down to 6.1 or 5.1, respectively...! [My guess: Don't expect real ".2" source material or receivers until two-lfe soundtracks become popular in movie theaters first.]

Someone already posted that we can do .2 just using a Y-cable and that is all 7.2 is! Dont be fooled into spending more money on 7.2 AVRs and do not even bother worrying about 7.2 at all. Its a waste of discussion, time and money.

Actually, I believe that some higher end receivers do left side/right side base redirection to left and right subs, so the Y-cable assertions are not exactly correct. But I suspect that most environments will not benefit from this [minor] enhancement...

[Home Office system schematic]"My AV systems were created by man. They evolved. They rebelled. There are many speakers. And they have . . . A PLAN."

What is the difference in the 2 sub outputs? That is, how is it derived since we only have .1 sources?

I used to think the 2 sub outs on the H/K 745 receiver contained stereo content, but from what I've read those outputs contain the same information (derived the typical way: filtering low frequencies from the main channels and adding LFE). However, the 2 outputs are EQ'd independently in order to get more consistent (not necessarily flatter) frequency response across multiple seats than is possible with a single sub.

Floyd Toole, Todd Welti and Sean Olive all work at Harman. You've probably seen the whitepapers they've published about using multiple subs to get consistent low frequency response throughout the room. No surprise that their research would end up influencing the subwoofer configuration and EQ systems of Harman receiver.

Other manufacturers, like Denon and Lexicon, actually have 3 different signals going to the 3 subwoofer outs on their pre-pros. The left sub out gets the bass filtered from all the left channels (front, surround, surround-back). Ditto the right sub out. As you've already guessed, the centre channel is split to both subs. The 3rd subwoofer output is for dedicated LFE duties, providing an extra kick for content that has a .1 channel. Of course, this sub goes silent when listening to sources that have no discrete LFE channel.

Actually, I believe that some higher end receivers do left side/right side base redirection to left and right subs, so the Y-cable assertions are not exactly correct. But I suspect that most environments will not benefit from this [minor] enhancement...

Yes, they will do left/right/Center but its really a pointless design when a sub system can simply handle all LFE stuff easily by itself and we all know that frequencies <= 80Hz are not localized anyways. This is like running your mains in LARGE mode and running the speaker wire through your sub amps first Heck, subs should not be placed with the mains anyways....this is honestly really dumb in my books.

To me it would just be more money wasted on something that is not needed. EQing options? No AVR will do better then a DCX2496.

Yes, they will do left/right/Center but its really a pointless design when a sub system can simply handle all LFE stuff easily by itself and we all know that frequencies <= 80Hz are not localized anyways.

Stereo subs aren't for bass localization but instead for low frequency envelopment. Check out the following paper (easier if you skip to the conclusion first, then go back to the begining).

I dont care about 2 channel listening at all so I will pass on any 2-channel discussion. 5.1, 7.1 discussion is more about Movies in my opinion and I do know that sub placement and EQing should be indedendant of any main speaker setup.

Someone already posted that we can do .2 just using a Y-cable and that is all 7.2 is! Dont be fooled into spending more money on 7.2 AVRs and do not even bother worrying about 7.2 at all. Its a waste of discussion, time and money.

I have 4 subs in a room to all requiring a connections, my sub has one Sub out RCA connection but I easily wire them all up properly. Also, sub calibration should ALWAYS be done outside of any Pre/pro or AVR using the proper sub EQing products available and posted all the time in the DIY sub or Subwoofer forums.

The subwoofer outputs (2) for the AVR 745 are different not the same output signal as one gets if they parallel all the subwoofer inputs with a single AVR subwoofer output..

As Sanjay mentioned...
Harman International has a corporate R & D team that does continual development for certain DSP areas such as Room EQ and multi-channel Matrix decoding. Next these IPs appear in various hardware and systems marketed under certain Harman brands, these include OE car audio systems in Mercedes, BMW, Lexus, Land Rover, Chrysler. Also certain higher end audio components branded Mark Levinson & Lexicon, all owned by Harman International as well as AVRs branded Harman/Kardon. Pretty simple to understand, once the R&D is done and final algorithms are validated these show up in various Harman branded components and systems.

Now back to the main feature of multiple subwoofers..
The R&D team under Dr.Toole, Dr.Olive and others..
Developed some incredible findings about using multiple subwoofers, check out the AES preprints and one will find alot of substantiation for this subject.

The Room EQ software within the AVR 745 was developed by the Harman R&D team. And it was explained to me that for each subwoofer, the AVR does a independent low frequency sweep from the listener's position. Then the DSP and its S/W calculates a unique independent output signal (transfer function) for each subwoofer independently. The basic idea is to correct for audible low frequency issues as heard while in the listener's position. Also the S/W is designed to pull down peaks rather than boost the EQ to fill holes as to save DSP headroom. Since every room has its own unique layout, size, furnishings, construction materials plus the physical positioning of each loudspeaker and subwoofer will vary. This is why there is such as a significant audible differences between every listening room, studio or auditorium even when using the same electronics and loudspeakers..

5.1, 7.1 discussion is more about Movies in my opinion and I do know that sub placement and EQing should be indedendant of any main speaker setup.

The stereo bass technique described in the research paper is more useful for music (2-channel or multi-channel) than movie soundtracks. With music, it gives a sense of spaciousness in the low frequencies that mimics what I've heard at live events. Whenever I've tried it with movies, I just end up with is less bass impact.

Anyway, all I was trying to say is that multiple subs are not "pointless". There are legitimate reasons to use more than one subwoofer. Stereo bass may not be something you want for movies, but getting consistent bass response at all listening positions is a worthy goal.

There are legitimate reasons to use more than one subwoofer. Stereo bass may not be something you want for movies, but getting consistent bass response at all listening positions is a worthy goal.

To obtain consistent bass response has nothing to do with stereo bass. I spent lots of time with that link and I have conclude its just a bunch of wind \\

to obtain proper bass in any room you need bass traps and enough subs properly located, its really that simple. Anyone buying AVRs to try and obtain consistent bass are just fooling themselves and wasting money. Again, nothing new around here

Let's say I'm interested in one or two eD a7-900, which is recommended to play material <40Hz. Unless, or even if, I have very capable full-range speakers throughout my system, I might want to use a less monstrous sub (a midbass module, as some have called it) to take charge between 40-80Hz. A Y-cable can't do this. A FBD can, if you want another piece of equipment in your system, and are willing to spend some time fiddling with a computer program to tweak it. If an auto-calibration program in your receiver can do this ((or make it simple to do yourself), it is a solution that many enthusiasts would appreciate.

7.2 on low to mid range receivers is the same as 7.1. As far as I know there is not content with 2 separate low frequency channels. Even if there is, frequencies under 100hz are omnidirectional. This meaning you won't be able to tell where the audio is coming from.

There is only one LFE channel in movies. However, having an AVR that can independently adjust two subs is a big plus. Too bad most midrange'ish AVRs simply provide two parallel outputs, leaving it to the user to align the subs for optimum response.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

Dont be fooled into spending more money on 7.2 AVRs and do not even bother worrying about 7.2 at all. Its a waste of discussion, time and money.
As far as I know there is not content with 2 separate low frequency channels , 7.2 on low to mid range receivers is the same as 7.1.

There is no two-channel LFE content as has been said. What the high-end AVRs offer is independent calibration and compensation of the second sub. Otherwise, listeners with two subs have to manually align one of them and then make sure they play well together, something usually requiring measurement gear (mic + REW or whatever).

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

My system is 7.3 (of-sorts).
In music-mode I get 2.2 (aka stereo bass), and in movie-mode I get .2 + the LFE track, going to 10 discrete subwoofers.
I coin it "tri-channel" bass.

Load audicity, create a 2-ch wav file each 180 degrees out of phase with a 30hz sinewave, convert this to Dobly 5.1 and play it on a ".2" capable system with mains set to small at 80hz.
If you system is only .1 you won't hear anything, it will cancel when summed (or at least it should if the AVR is processing it correctly).

Load audicity, create three wav files each 60 degrees out of phase with a 20hz, 40hz, and 30hz sinewave, convert this to Dobly 5.1 and play it on a ".3" capable with the mains set to small at 80hz. system.
Again, you will hear three discrete tones with different woofer excursions.
On a .1 system all woofers will have the same excursion and the 20 and 30hz will mostly cancel when summed (because they are 60*3 or 180 degrees out of phase).

Now whether or not movie directors take advantage of that technology and put it on a disc is entirely another matter.
Technically you could continue this for all 8 channels, one might consider that important if your sides, rears and center can't do 20hz or less with authority.

Obviously a "real" .3 LFE would be an entirely different concept and not compliant with 2-ch stereo bass CD's or 99.999% of existing AVR's and Dolby/DTS chips.

My system is 7.3 (of-sorts).
In music-mode I get 2.2 (aka stereo bass), and in movie-mode I get .2 + the LFE track, going to 10 discrete subwoofers.
I coin it "tri-channel" bass.

Load audicity, create a 2-ch wav file each 180 degrees out of phase with a 30hz sinewave, convert this to Dobly 5.1 and play it on a ".2" capable system with mains set to small at 80hz.
If you system is only .1 you won't hear anything, it will cancel when summed (or at least it should if the AVR is processing it correctly)

Clip....[\quote]

I think that is the best case I've read against anything >.1 yet... If I understand correctly... If I wire my subs wrong, have them spaced wrong, do any of many MANY different things other than set it up perfectly right... I'm going to not just be inferior to an 6.1 or 7.1 system, it will be like I have a 6.0 or 7.0 system with a bipolar canceling failure. That is both funny, sad, and scarry.

Someone already posted that we can do .2 just using a Y-cable and that is all 7.2 is! Dont be fooled into spending more money on 7.2 AVRs and do not even bother worrying about 7.2 at all. Its a waste of discussion, time and money.